Efficient reduction of fibrous capsule formation around silicone breast implants densely grafted with 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers by heat-induced polymerization.

Implants based on silicone elastomers, polydimethylsiloxane (PDMS), have been widely used for breast augmentation and reconstruction, but excessive foreign body reactions around implants often cause serious side effects such as capsular contracture. In our previous study, we covalently grafted 2-methacryloyloxyethyl phosphorylcholine (MPC)-based polymers on the surface of PDMS blocks by UV-induced polymerization and showed effective reduction of capsular formation around the MPC-grafted PDMS in rats. In the present study, we examined the efficacy of heat-induced polymerization of MPC grafting on silicone breast implants intended for humans, and analyzed the in vivo inhibitory effect against capsular formation and inflammation in pigs, which are closely related to humans in terms of epidermal structures and fibrotic processes. The heat-induced polymerization provided a thicker MPC-grafted surface and was more effective than UV-induced polymerization for the grafting of complex shaped non-transparent implants. After 24-week implantation in the submuscular pockets of Yorkshire pigs, the heat-induced MPC-grafted breast implants showed 45% smaller capsular thickness and 20-30% lower levels of inflammatory markers such as myeloperoxidase (MPO), transforming growth factor-β (TGF-β), and α-smooth muscle actin (α-SMA) in surrounding tissues compared to non-grafted implants. This study provides important information for future clinical trials of MPC-grafted silicone implants.